Seal ring formation is an important part in the back-end of semiconductor processes. Seal rings are stress protection structures around integrated circuits, which protect the internal circuit inside semiconductor chips from damage caused by the sawing of the semiconductor chips from wafers.
Typical seal rings are usually formed of interconnected metal lines and connecting vias. FIG. 1 is a schematic view of a part of seal ring 10, which is formed on an inner side of scribe line 12, sometimes also referred to as dicing line 12. Typically, there is a circuit region (not shown) on the left-hand side of the drawing.
Seal ring 10 includes interconnected metal components, which are formed of metal lines 14 and conductive vias 18, both formed in dielectric layers 16. Metal lines 14 and vias 18 are physically connected. Moreover, passivation film 20 is formed over a top layer of seal ring 10.
Because of the provision of seal ring 10 and passivation film 20, the circuit region on the inner side of seal ring 10 is protected from influences of external environments, which may cause cracking in the semiconductor chips, thus it is possible to ensure stability of properties of the semiconductor device over a long period of time. Typically, seal rings may be electrically grounded. To have greater strength, vias 18 may be interconnected, forming a continuous via bar, as shown in FIG. 2.
A further function of seal ring 10 is to protect the integrated circuits on the inner side of seal ring 10 from moisture-induced degradation. Dielectric layers 16 are typically formed of porous low-k dielectric materials. Moisture can easily penetrate through low-k dielectric layers 16 to reach the integrated circuits. Since seal ring 10 is formed of metal, it blocks the moisture penetration path and may substantially eliminate any moisture penetration.
Although continuous via bars 18, combined with metal lines 14, can protect cracking from extending into circuit regions, the conventional seal rings suffer drawbacks. First, conventionally, only one seal ring with a continuous via bar is formed. If this seal ring is damaged, there will be no structure for preventing cracks from propagating into the respective semiconductor chip. Second, the continuous via bars often have widths substantially less than the thickness of the respective overlying metal lines, and hence do not have enough strength to stop crack propagation during die sawing. Third, the cracks may propagate through interface 22 between passivation film 20 and the underlying layer into the circuit regions. New structures and formation methods are thus needed.